浆料喷雾干燥法制备球形锰酸锂正极材料及其改性研究

发布时间：2018-05-14 19:18

本文选题：锰酸锂 + 喷雾干燥法　；参考：《中南大学》2011年博士论文

【摘要】：提高电池性能和降低电极材料的成本一直是锂离子电池的主要研发方向。尖晶石型LiMn2O4具有工作电压高、安全性能好、生产成本低、对环境友好等特点,是21世纪最具发展前景的锂离子电池正极材料之一。但尖晶石型LiMn2O4的比容量较低,电化学循环性能较差阻碍其规模化应用。所以如何通过改性提高尖晶石LiMn2O4材料的电化学性能是其得以广泛应用的关键。因此,探寻新的合成及改性方法成为了尖晶石LiMn2O4材料改性研究的热点。为了获得物理加工和电化学性能优异的锰酸锂正极材料,本文从工业化角度出发,提出采用浆料喷雾干燥法制备球形掺铬锰酸锂,并进行了系列表面包覆改性研究。首先对浆料喷雾干燥法制备球形锰酸锂的工艺条件进行了初步研究。结果发现,采用淀粉做为粘结剂时,喷雾干燥后样品颗粒球形度好,不易破碎；控制制浆固含量为50%时,所得浆料均匀、流动性好,得到喷雾干燥产物粉体平均颗粒大小在20μm左右；喷雾干燥过程中温度的控制直接影响到干燥效果和干燥样品的物理性质。干燥后得到球形前驱体制备锰酸锂的最佳焙烧温度为770℃,此时得到样品的初始放电容量为122.1 mAh·g-1,循环30次后容量保持率为89.8%。与普通干燥法相比,浆料喷雾干燥法制备的球形材料在形貌、电化学阻抗、放电容量和循环性能等方面有较大的优势。其次,系统研究了不同锰源对浆料喷雾干燥法制备锰酸锂性能的影响。通过热处理和酸处理的方式对现有电解二氧化锰(EMD)进行结构和组份优化。结果发现,将EMD在300-400℃进行适当的热处理,可以优化其结构,使其有利于嵌锂并顺利实现向锰酸锂的转化,得到的产物在初始放电容量和循环性能上都有所提高。而酸处理能有效减少EMD中钠、硫杂质的含量,使产物锰酸锂中杂质含量也降低,产物的初始放电容量得到提高,但是循环性能还需要改善。精制化学二氧化锰(CMD)的结构与360℃热处理后EMD相似。CMD制备得到尖晶石锰酸锂的初始放电容量为120.0 mAh·g-1,循环40次后放电容量保持为100.8 mAh·g-1,容量保持率为84.0%。四氧化三锰做锰源制备的锰酸锂电化学性能最佳,0.2C首次放电容量达127.9mAh·g-1,2C放电容量为124.7 mAh·g-1,40次充放电循环后容量保持率达到97.6%,但是物理性能相对较差。综合比较EMD、CMD和四氧化三锰等锰源制备的锰酸锂的物理和电化学性能,300-400℃热处理后EMD应用前景最佳。然后深入研究了浆料喷雾干燥法制备掺铬锰酸锂,发现采用醋酸铬和硫酸铬等可溶性铬盐,铬离子可以浸渍进入二氧化锰空隙,在混合过程即可形成均匀的前驱体,因此得到的样品与采用三氧化二铬制备的样品相比晶格参数和晶胞体积小,电荷转移阻抗小,电化学极化小。使用醋酸铬为铬源,掺铬量x=0.04时,制得的锰酸锂高温电化学性能最佳,在55℃条件下进行充放电测试,得到初始放电容量为117.2 mAh·g-1,循环30次后容量保持率为93.3%。最后,为了更进一步改善锰酸锂的高温循环性能,分别采用三种包覆方法对上述制得的球形掺铬锰酸锂进行了表面包覆改性研究。其中,水溶胶法包覆氧化铝,成本低,环境友好,得到产物包覆效果好,包覆1%的Al2O3得到的包覆产物初始放电容量为114.5 mAh·g-1,高温循环50次后容量保持率为93.6%。低热固相法包覆氧化铝工艺更简单,能耗更低,更适合于工业放大,同样包覆1%的Al2O3得到的包覆产物初始放电容量为115.6 mAh·g-1,50次高温循环容量保持率为92.8%。除了包覆氧化物外,还首次对多元醇法包覆磷酸盐进行了尝试,并取得了较好的成效,磷酸盐包覆材料表现出更好的稳定性,使得材料的高温循环稳定性得到较大提高,其中包覆了磷酸钴锂的球形掺铬锰酸锂样品,其首次放电比容量为117.8 mAh·g-1,经50次高温循环后放电比容量仍然保持为114.0 mAh·g-1,容量保持率提高为96.8%。相比未包覆材料初始放电容量为117.1 mAh·g-1,50次高温循环后容量保持率只有90.3%,包覆后材料的循环稳定性能都得到较大提高。
[Abstract]:Improving the battery performance and reducing the cost of electrode materials is the main research direction of lithium ion batteries. The spinel type LiMn2O4 has the characteristics of high working voltage, good safety, low production cost and friendly environment. It is one of the most promising lithium ion battery positive materials in twenty-first Century. But the specific capacity of the spinel type LiMn2O4 is low. The poor electrochemical performance hinders its large-scale application. So how to improve the electrochemical properties of spinel LiMn2O4 material by modification is the key to its wide application. Therefore, exploring new synthesis and modification methods has become a hot topic in the research of spinel LiMn2O4 material modification. In this paper, the preparation of spherical chromium manganese doped lithium manganese acid by slurry spray drying is proposed in this paper, and a series of surface coating modification studies have been carried out.
The process conditions for preparing spherical lithium manganate by spray drying were first studied. The results showed that when starch was used as binder, the sphericity of the particles was good and it was not easy to break after the spray drying. When the solid content of the pulp was 50%, the size of the slurry was uniform, the flow property was good, and the average particle size of the powder of the spray drying product was obtained. At about 20 mu m, the temperature control in the spray drying process directly affects the drying effect and the physical properties of the dry samples. The optimum calcination temperature of the lithium manganate prepared by the spherical precursor system is 770 C after drying, and the initial discharge capacity of the sample is 122.1 mAh. G-1, and the retention rate of the capacity is 89.8%. and ordinary drying after 30 cycles. Compared with the method, the spherical material prepared by slurry spray drying has great advantages in morphology, electrochemical impedance, discharge capacity and cycle performance.
Secondly, the effects of Different Manganese Sources on the properties of lithium manganese dioxide prepared by slurry spray drying were systematically studied. The structure and composition of the existing electrolytic manganese dioxide (EMD) were optimized by heat treatment and acid treatment. The results showed that the proper heat treatment of EMD at 300-400 C could be used to optimize its structure and make it good for lithium intercalation and smooth solid. The conversion of lithium manganate can improve the initial discharge capacity and cycle performance, and acid treatment can effectively reduce the content of sodium and sulfur impurities in EMD, reduce the impurity content in the product of lithium manganate, increase the initial discharge capacity of the product, but also improve the cycle performance. Refined chemical manganese dioxide (CMD). The initial discharge capacity of spinel lithium manganate is 120 mAh. G-1, and the discharge capacity is kept at 100.8 mAh. G-1 after 40 cycles. The capacity retention rate is the best in 84.0%. four oxidation three manganese manganese source, and the first discharge capacity of 0.2C is up to 127.9mAh g-1,2C discharge, and the initial discharge capacity of 0.2C is up to 127.9mAh g-1,2C discharge. The initial discharge capacity of spinel manganic acid is prepared by the structure and EMD after heat treatment at 360. After the capacity of 124.7 mAh / g-1,40 secondary charge discharge cycle, the capacity retention rate is 97.6%, but the physical performance is relatively poor. The physical and electrochemical properties of lithium manganate prepared by EMD, CMD and four manganese manganese manganese and other manganese oxides are compared synthetically, and the application of EMD is the best after the heat treatment at 300-400.
Then, the preparation of chromium doped lithium manganese acid by the slurry spray drying method is studied. It is found that the chromium ions can be impregnated into the gap of manganese dioxide by using chromium acetate and chromium sulfate, and the homogeneous precursor can be formed in the mixing process. So the obtained samples are compared with the lattice parameters and cell bodies compared with the samples prepared by the three oxidation of two chromium. When the product is small, the charge transfer impedance is small and the electrochemical polarization is small. When chromium acetate is used as the chromium source and the chromium content is x=0.04, the high temperature electrochemical performance of lithium manganate is the best. The charge discharge test is carried out at 55 centigrade, the initial discharge capacity is 117.2 mAh. G-1, and the capacity retention rate is 93.3%. after 30 cycles.
Finally, in order to further improve the high temperature cycling performance of lithium manganate, three kinds of coating methods were used to study the surface coating modification of the spherical chromium manganese doped lithium manganese dioxide, of which the hydrosol was coated with alumina, the cost was low, the environment was friendly, the coating effect of the product was good, and the coating product of the coated 1% Al2O3 was initially placed. The capacitance is 114.5 mAh. G-1, and the capacity retention after 50 times high temperature cycle is 93.6%. low heat solid phase coating alumina process is simpler, energy consumption is lower, and it is more suitable for industrial enlargement. The initial discharge capacity of coated products with 1% Al2O3 coating is 115.6 mAh. G-1,50 secondary high temperature cycle capacity retention rate is 92.8%. except coated oxide. It is also the first time to try to cover phosphate with polyol method, and good results have been achieved. The phosphate coating material shows better stability and the high temperature cycle stability of the material is greatly improved, in which the spherical lithium manganese phosphate lithium manganese phosphate sample is coated with a specific capacity of 117.8 mAh. G-1 for the first time, and 50 times higher. After the temperature cycle, the discharge specific capacity remains 114 mAh. G-1, the capacity retention rate is increased to 96.8%. compared with the initial discharge capacity of the uncoated material of 117.1 mAh. G-1,50 secondary high temperature cycle, the capacity retention rate is only 90.3%, and the cyclic stability performance of the material after coating is greatly improved.

【学位授予单位】：中南大学
【学位级别】：博士
【学位授予年份】：2011
【分类号】：TM912

【相似文献】